1. Field of the Invention
The present invention generally relates to a constant velocity universal joint of the tripod type, and more particularly to low friction type tripod joints.
2. Background Art
Generally, conventional tripod-type constant velocity (CV) universal joints utilize an outer drive member formed with three arc-shaped track grooves extending axially at equally spaced circumferential positions, and an inner part having three trunnions extending radially so as to correspond to the track grooves of the outer drive member. A roller element is rotatably mounted on each trunnion. Each roller element is received in a track groove so as to produce a rolling motion in the axial direction so that a rotary force is transmitted between shafts connected to the inner and outer drive members.
However, conventional tripod type CV joints generally experience difficulty when the shafts are articulated with respect to each other, i.e., form a working angle. In this situation, the roller elements become inclined with respect to the track groove thereby causing relative sliding between the roller element and track groove without continuous rolling motion. As a result, a large frictional resistance acts on the trunnion and the roller element.
In one known CV joint arrangement disclosed in JP 59-40016, the trunnions are formed with an outer spherical receiving surface and a roller assembly formed from a freely oscillating cylindrical guide ring mounted about the trunnion, an outer ring which engages the inside of a groove in the outer drive member, and a plurality of rolling bodies are disposed between the outer and guide rings.
A similar CV joint arrangement is disclosed in U.S. Pat. No. 5,411,440 to Bensinger et al. More, specifically, according to the ""440 patent, a CV universal joint of the tripod type is provided having an outer joint part formed with three circumferentially distributed, axially extending longitudinal recesses, and an inner joint part formed with three circumferentially distributed radial journals engaging the longitudinal recesses. The journals are provided with roller members which are held substantially isogonally in the longitudinal recesses and which are held relative to the journals so as to be radially displaceable and angularly movable. Each roller member is rotatably supported on a roller carrier having a cylindrical inner surface. The journals have spherical pivot heads which engage the radial cylindrical inner surface of a roller carrier so as to be radially movable and angularly movable at right angles thereto around two axes.
With both arrangements, the spherical surface of the journal heads pivot relative to the inner cylindrical surface of the roller member to maintain the roller member parallel to the groove of the outer drive member even if the joint is articulated, thereby reducing frictional resistance. However, the contour of the spherical journal head and inner cylindrical ring only allows contact at a limited surface region. This in turn causes concentration of Hertzian forces at a small contact region, and increases the potential for higher friction and shuddering of the joint during operation.
Therefore, a need exists for a CV joint of the tripod type which can maintain the roller assemblies in a parallel orientation relative to the outer part grooves and overcome the deficiencies in known arrangements.
Therefore, it is an object of the present invention to provide an anti-shudder CV joint of the tripod type having a journal head that pivots and rotates within a roller member, where the contact surface between a journal and roller member is arranged to distribute the contact force across a larger contact surface area.
In accordance with this and other objects, the present invention provides a constant velocity universal joint of a tripod type including an outer joint member having three circumferentially distributed, axially extending longitudinal tracks formed therein, and an inner joint member having three circumferentially distributed radial journals arranged to engage the longitudinal tracks. Each journal is provided with an outer spherical end surface. A roller member is mounted about the outer end surface of each journal and arranged to contact opposing inner surfaces of a track, wherein each roller member includes an inner ring having a spherical inner surface arranged to nest about the outer spherical end surface of a journal so as to allow the journal to pivot therein and maintain the roller member in a parallel orientation relative to the track upon articulation of the joint.
In accordance with one embodiment of the present invention, the opposing sides of the longitudinal tracks are concave, and each roller member includes a rotatable outer ring having a spherical outer surface in a region of contact with the opposing sides of a track. In another embodiment, the opposing sides of the longitudinal tracks are shaped as a Gothic arch, and each roller member includes a rotatable outer ring having an outer surface in the shape of a truncated ellipse or prolate spheroid in a region of contact with the opposing sides of a track.
In accordance with one aspect of the present invention, the inner ring of the roller member is moveable to allow the inner ring to stay properly positioned relative to the journal as the journal pivots therein.
Thus, the present invention provides an anti-shudder constant velocity universal joint of the tripod type having an outer joint member including three circumferentially distributed, axially extending longitudinal recesses or tracks formed therein, and an inner joint member having three circumferentially distributed radial journals arranged to engage the longitudinal tracks when the joint is assembled. The outer and inner members are connected to respective shafts. The end of each journal is mated with and supports rotation of a roller bearing assembly. The journals hold the roller bearing assemblies in a respective longitudinal track relative to the journal. The CV joint of the present invention is particularly suited for use with articulated joints, i.e., a joint in which the shafts connected to the outer and inner joint members form an angle with respect to each other when the joint is assembled. Large frictional forces on the roller bearings created by such an articulated joint are prevented because the joint is able to maintain the roller bearings in a relatively proper/parallel orientation within the longitudinal tracks by allowing the journal ends to freely rotate and pivot within an inner ring of the roller bearing assembly. A spherical-to-spherical contact surface is provided between the journal ends and respective roller bearing assemblies to lower Hertzian stresses by distributing forces over a larger region of contact.
The above features and advantages of the present invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.